Require Go 1.20

[contrast-jproberts]

gogs/gogs@4821e89 upgraded a dependency which now uses errors.Join, a function introduced in go1.20 . This is now the minimum supported version to build gogs from source.

[contrast-jproberts]

I was able to confirm the version support using docker run --rm -it golang:1.19 and following the steps in https://github.com/gogs/docs/blob/master/en-US/installation/install_from_source.md#compile-gogs . The build fails with the following output

root@82b1254a7695:/go/gogs# go build -o gogs
# github.com/editorconfig/editorconfig-core-go/v2
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/cached_parser.go:63:21: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/config.go:29:16: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/config.go:76:21: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/definition.go:48:20: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/definition.go:61:20: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/definition.go:75:20: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/editorconfig.go:92:21: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/editorconfig.go:214:16: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/editorconfig.go:241:16: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/editorconfig.go:258:16: undefined: errors.Join
../pkg/mod/github.com/editorconfig/editorconfig-core-go/v2@v2.6.0/editorconfig.go:258:16: too many errors
note: module requires Go 1.20

I then followed the same steps inside docker run --rm -it golang:1.20 and the build succeeded.